/*
 * Copyright (c) 1985, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Portions copyright (c) 1999, 2000
 * Intel Corporation.
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 * 
 *    This product includes software developed by the University of
 *    California, Berkeley, Intel Corporation, and its contributors.
 * 
 * 4. Neither the name of University, Intel Corporation, or their respective
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS, INTEL CORPORATION AND
 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING,
 * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS,
 * INTEL CORPORATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

#ifndef lint
static char sccsid[] = "@(#)pow.c	8.1 (Berkeley) 6/4/93";
#endif /* not lint */

/* POW(X,Y)
 * RETURN X**Y
 * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
 * CODED IN C BY K.C. NG, 1/8/85;
 * REVISED BY K.C. NG on 7/10/85.
 * KERNEL pow_P() REPLACED BY P. McILROY 7/22/92.
 * Required system supported functions:
 *      scalb(x,n)
 *      logb(x)
 *	copysign(x,y)
 *	finite(x)
 *	drem(x,y)
 *
 * Required kernel functions:
 *	exp__D(a,c)			exp(a + c) for |a| << |c|
 *	struct d_double dlog(x)		r.a + r.b, |r.b| < |r.a|
 *
 * Method
 *	1. Compute and return log(x) in three pieces:
 *		log(x) = n*ln2 + hi + lo,
 *	   where n is an integer.
 *	2. Perform y*log(x) by simulating muti-precision arithmetic and
 *	   return the answer in three pieces:
 *		y*log(x) = m*ln2 + hi + lo,
 *	   where m is an integer.
 *	3. Return x**y = exp(y*log(x))
 *		= 2^m * ( exp(hi+lo) ).
 *
 * Special cases:
 *	(anything) ** 0  is 1 ;
 *	(anything) ** 1  is itself;
 *	(anything) ** NaN is NaN;
 *	NaN ** (anything except 0) is NaN;
 *	+(anything > 1) ** +INF is +INF;
 *	-(anything > 1) ** +INF is NaN;
 *	+-(anything > 1) ** -INF is +0;
 *	+-(anything < 1) ** +INF is +0;
 *	+(anything < 1) ** -INF is +INF;
 *	-(anything < 1) ** -INF is NaN;
 *	+-1 ** +-INF is NaN and signal INVALID;
 *	+0 ** +(anything except 0, NaN)  is +0;
 *	-0 ** +(anything except 0, NaN, odd integer)  is +0;
 *	+0 ** -(anything except 0, NaN)  is +INF and signal DIV-BY-ZERO;
 *	-0 ** -(anything except 0, NaN, odd integer)  is +INF with signal;
 *	-0 ** (odd integer) = -( +0 ** (odd integer) );
 *	+INF ** +(anything except 0,NaN) is +INF;
 *	+INF ** -(anything except 0,NaN) is +0;
 *	-INF ** (odd integer) = -( +INF ** (odd integer) );
 *	-INF ** (even integer) = ( +INF ** (even integer) );
 *	-INF ** -(anything except integer,NaN) is NaN with signal;
 *	-(x=anything) ** (k=integer) is (-1)**k * (x ** k);
 *	-(anything except 0) ** (non-integer) is NaN with signal;
 *
 * Accuracy:
 *	pow(x,y) returns x**y nearly rounded. In particular, on a SUN, a VAX,
 *	and a Zilog Z8000,
 *			pow(integer,integer)
 *	always returns the correct integer provided it is representable.
 *	In a test run with 100,000 random arguments with 0 < x, y < 20.0
 *	on a VAX, the maximum observed error was 1.79 ulps (units in the
 *	last place).
 *
 * Constants :
 * The hexadecimal values are the intended ones for the following constants.
 * The decimal values may be used, provided that the compiler will convert
 * from decimal to binary accurately enough to produce the hexadecimal values
 * shown.
 */

#include <errno.h>
#include <math.h>

#include "mathimpl.h"

#if (defined(vax) || defined(tahoe))
#define TRUNC(x)	x = (double) (float) x
#define _IEEE		0
#else
#define _IEEE		1
#define endian		(((*(int *) &one)) ? 1 : 0)
#define TRUNC(x) 	*(((int *) &x)+endian) &= 0xf8000000
#define infnan(x)	0.0
#endif		/* vax or tahoe */

const static double zero=0.0, one=1.0, two=2.0, negone= -1.0;

static double pow_P __P((double, double));
#pragma warning (disable:4723)
double pow(x,y)
double x,y;
{
	double t;

    /* This test needs to be first for EFI because the compiler
        doesn't check for unordered comparisons */
    if (isnan(y)) return (y);                       /* y is NaN */

    if (y==zero) return (one);                      /* if y is 0 */

	if (y==one || isnan(x)) return (x);             /* if x is NaN or y=1 */

    if (!finite(y))	{	/* if y is INF */
		if ((t=fabs(x))==one) return (y - y);	    /* +-1 ** +-INF is NaN */
			
		if (t>one) return ((y<0)? zero : ((x<zero)? y-y : y));
		else return ((y>0)? zero : ((x<0)? y-y : -y));
    }

	if (y==two) return (x*x);                       /* x ** 2 */

	if (y==negone) return (one/x);                  /* x ** -1 */

    /* x > 0, x == +0 */
    if (copysign(one, x) == one) {
        return (pow_P(x, y));
    }
    /* sign(x)= -1 */
	/* if y is an even integer */
    t=drem(y,two);
    if (t == zero) {
        return (pow_P(-x, y));
    }
	/* if y is an odd integer */
    if (copysign(t,one) == one) {
        return (-pow_P(-x, y));
    }
	/* Henceforth y is not an integer */
	if (x==zero) return ((y>zero)? -x : one/(-x));	/* x is -0 */

    if (_IEEE) return (zero/zero);

	return (infnan(EDOM));
}

/* kernel function for x >= 0 */
static double
#ifdef _ANSI_SOURCE
pow_P(double x, double y)
#else
pow_P(x, y) double x, y;
#endif
{
	struct Double s, t, __log__D();
	double  __exp__D();
	volatile double hugeval = 1e300, tiny = 1e-300;

    if (x == zero) {
		if (y > zero) return (zero);
#if !defined(EFI32) && !defined(EFI64) && !defined(EFIX64)
        if (_IEEE) return (hugeval*hugeval);
#else
		if (_IEEE) return (one/zero);
#endif
		return (infnan(ERANGE));
    }
    if (x == one) return (one);
    if (!finite(x)) {
        if (y < zero) return (zero);
#if !defined(EFI32) && !defined(EFI64) && !defined(EFIX64)
        if (_IEEE) return (hugeval*hugeval);
#else
		if (_IEEE) return (one/zero);
#endif
		return (infnan(ERANGE));
    }
    if (y >= 7e18) {		/* infinity */
		if (x < 1) return(tiny*tiny);
#if !defined(EFI32) && !defined(EFI64) && !defined(EFIX64)
        if (_IEEE) return (hugeval*hugeval);
#else
		if (_IEEE) return (one/zero);
#endif
		return (infnan(ERANGE));
    }
	/* Return exp(y*log(x)), using simulated extended */
	/* precision for the log and the multiply.	  */

	s = __log__D(x);
	t.a = y;
	TRUNC(t.a);
	t.b = y - t.a;
	t.b = s.b*y + t.b*s.a;
	t.a *= s.a;
	s.a = t.a + t.b;
	s.b = (t.a - s.a) + t.b;
	return (__exp__D(s.a, s.b));
}
#pragma warning (default:4723)
